Towel bar - Al Alloy - Modern Times - France

Towel bar - Al Alloy - Modern Times - France

Towel bar

Christian. Degrigny (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland)

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Credit HE-Arc CR, J.Schröter.

Fig. 1: Front and back sides of a towel bar,

Towel bar with traces of use and a broken section (Fig. 1). White deposits have developed on the metal surface. Dimensions: L = 45cm.

Household implement

Château de Germolles, Mellecey, Bourgogne, France

Unknown

Modern Times

20th century

Indoor atmosphere

Château de Germolles, Mellecey, Bourgogne

Château de Germolles, Mellecey, Bourgogne

None

N/A

Complementary information

None.

Credit HE-Arc CR, J.Schröter.

Fig. 2: Detail of the back side of the towel bar showing the location of the sampling area,

None.

Credit HE-Arc CR, S.Ramseyer.

Fig. 3: SEM image of the cross-section of the fragment sampled from the towel bar showing the location of Fig. 4,

Sample cut from the back side of the towel bar (Fig. 2).

Al Alloy

Unknown

None

HE-Arc CR, Neuchâtel, Neuchâtel

HE-Arc CR, Neuchâtel, Neuchâtel

2017, EtICAL project (Study of corrosion forms of aluminium alloys from Swiss public collections)

Complementary information

None.

Analyses performed: 
Metallography, SEM/EDS.

None.

The metal is a relatively pure aluminium alloy with numerous inclusions (Fig. 4). From their chemical composition they can be interpreted as Al3Fe intermetallic compounds (Fig. 5). Pitting corrosion as well as a start of intergranular corrosion developing locally under the deposits, outlining some of the grains (Fig. 4). 

Credit HEI Arc, S.Ramseyer.

Fig. 4: SEM image of the metal sample from Fig. 3 (detail), BSE-mode. We observe the presence of numerous inclusions,

Credit HEI Arc, S.Ramseyer.

Fig. 5: EDS spectrum of the inclusions of Fig. 4,

Recrystallized grain structure

Al

Fe

Complementary information

None.

A very thin and loose oxide film has formed on the metal surface (CP1) and is locally covered by white deposits (D1). Intergranular corrosion has developed under the deposits (Fig. 6). EDS-SEM analysis indicates that the oxide layer rich in Al and O is contaminated with P and Si (area 1 on Fig. 6 and Fig. 7). These elements are even more present at the interface between CM1 and CP1 with Cl and S (area 2 on Fig. 6 and Fig. 8). The concentration of P and Si decreases in CM1 (area 3 on Fig. 6 and Fig. 9) while the concentration of S and Cl increases (Fig. 10). The deposit is mainly constituted of Ca, O, C and Si (probably CaCO3 and SiO2, area 4 on Fig. 6 and Fig. 11).

Credit HEI Arc, S.Ramseyer.

Fig. 6: SEM picture with location of EDS analyses of areas 1 to 4, BSE-mode. From bottom to top: the metal (M1) in light grey, the corroded metal (CM1), CP1 and D1. It can be compared to the stratigraphy representation of Fig. 12,

Credit HEI Arc, S.Ramseyer.

Fig. 7: EDS spectrum of area 1 of Fig. 6,

Credit HEI Arc, S.Ramseyer.

Fig. 8: EDS spectrum of area 2 of Fig. 6,

Credit HEI Arc, S.Ramseyer.

Fig. 9: EDS spectrum of area 3 of Fig. 6,

Credit HEI Arc, S.Ramseyer

Fig. 10: EDS Linescan from CM1 to M1,

Credit HEI Arc, S.Ramseyer.

Fig. 11: EDS spectrum of area 4 of Fig. 6,

Multiform - intergranular

Unknown

Complementary information

None.

Fig. 12: Stratigraphic representation of the fragment sampled from the towel bar in cross-section (SEM-BSE) using the MiCorr application. The characteristics of the strata are only accessible by clicking on the drawing that redirects you to the search tool by stratigraphy representation. This representation can be compared to Fig. 6, Credit HE-Arc CR, C.Degrigny.

None.

This aluminium alloy has a composition similar to a primary aluminium with an Al content between 99 and 99.8 mass%. The main impurity is Fe forming intermetallic (Al3Fe) inclusions. It is covered by a thin oxide layer (probably aluminium oxide). Pitting corrosion has formed under calcareous white deposits. It seems to develop as intergranular corrosion.

References on object and sample

References object
1. Degrigny, C. (2018) Etude, identification des objets en aluminium patrimoniaux et classification de leurs formes de corrosion - projet EtICAL, rapport interne HE-Arc CR.
2. Degrigny, C. and Schröter, J. (2019) Aluminium alloys in Swiss public collections: identification and development of diagnostic tools to assess their condition, in Metal 2019, proceedings of the ICOM-CC Metal WG interim meeting, eds. C. Chemello, L. Brambilla, E. Joseph, Neuchâtel (Switzerland), 408-415.

References sample
3. Degrigny, C. (2018) Etude, identification des objets en aluminium patrimoniaux et classification de leurs formes de corrosion - projet EtICAL, rapport interne HE-Arc CR.